Zakład Fizyki Wysokich Ciśnień - publikacje

Abstract: Neutron diffraction (ND) and inelastic incoherent neutron scattering (IINS) spectra in the 10 to 500 cm−1 region of the monoclinic and orthorhombic forms of m‐nitrophenol crystals in powder form are measured in the 90 to 370 K temperature range. The thermal expansion tensor elements for the two polymorphs are calculated from the ND data concerning the changes of lattice parameters. The principal coefficients of the tensors at 280 K are: α11 = 76.3, α22 = 137.0, and α33 = 13.0 (in 10−6 K−1) for the orthorhombic crystal and α11 = 72.8, α22 = 120.2, and α33 = 6.9 (in 10−6 K−1) for the monoclinic one. Also the direct dilatometric measurements on the single crystals of the two polymorphs along the b‐ and c‐axes are performed and the results of both methods are compared. The IINS spectra are compared with the previously measured IR and Raman spectra. A summary of the spectroscopic results is given and some attempts are made to explain the thermal expansion anisotropy in terms of hydrogen bonding and intramolecular charge transfer in both polymorphs. Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA